Aerospace and Electronic Systems Magazine August 2017 - 7

Ahluwalia and Singh
airband radio or satellite.3 On board an airplane there is a Satellite Data Unit (SDU)
that allows the air/ground communication
capability of the aircraft via a satellite network. It is supposed to be an integral part
of an aircraft's SATCOM system. It connects the aircraft with a satellite via ordinary radio frequency communication to
pass information, and the satellite in turn
connects to a ground station to pass the
same information or vice versa. The SDU
also communicates with an onboard multipurpose disk drive unit that is supposed to
maintain an updated list of ground stations
in the vicinity of the aircraft and allocates
an order of preference for selection of the
ground station to be used and in turn decides the choice of satellite. Besides continuously analyzing the data received from
all ground stations, the SDU also receives
information on the aircraft's position and
orientation from another system fitted on
board known as Air Data/Inertial Refer- Figure 1.
ence Unit. This information it passes to the Communication network of aircraft with satellites and ground stations.
Beam Steering Unit that directs the signal
beam from the aircraft to the satellite that has been chosen. Figure 1
RECOMMENDATIONS
shows the communication network generally existing between aircraft
The study of the causes of accidents led to recommendations for
and ground stations through satellites or directly with them.
several minor modifications and additions to the existing onboard
avionics; aircraft structure, software, and mechanical systems, and
to standard operating procedures that could, if implemented by
HANDSHAKE
the aviation industry, reduce the loss of human life and damage to
Whilst en-route, when the SDU is powered on and it attempts to conproperty associated with en-route aircraft accidents.
nect with the satellite network, it transmits a log-on request, which
is acknowledged by the ground station. This indicates that the particular SDU belongs to an active service subscriber and in turn also
REDUCE HANDSHAKE TIME
determines which satellite should be used to transmit messages to
that SDU. After connecting, if a ground station does not receive any
Keeping in mind the speed at which the passenger aircraft travels,
contact from a terminal for one hour, then the ground station transthe period of 15 minutes is considered to be a long gap. Consider that
mits a "log-on interrogation" message that is informally referred as
if the speed of the aircraft is 600 knots then in 15 minutes it would
a "ping". To this, an active terminal automatically responds. This
cover a distance of about 150 nautical miles, and this gap is a very
process of interrogating the terminal is known as a "Handshake".
long gap, in which any mishap can take place. It is therefore suggestAs a consequence of the Malaysia Airlines Flight MH 370 incident,
ed that, to ensure that an aircraft is tracked in real time, this period of
the international community deliberated for a long time about the
handshake should be reduced to 5 minutes in normal circumstances
duration of the wait before initiating a handshake, and reportedly a
and in the case of a shift in scheduled/intended flight path by over
proposal to reduce this time to 15 minutes is being deliberated.
20% then this period needs to be further reduced to 20 seconds and
may be termed as "Emergency Handshake System". This could be
3
automatically programmed in the onboard flight management sysOne of the important functions of ACARS is to automatically
detect and report changes to the major flight phases: G1, G2, G3,
tem. The information about a change in flight path/plan should also
G4, respectively. Out of the gate, Off the ground, On the ground,
be immediately and automatically communicated to other ground
and Into the gate is referred as OOOI in the aviation field. Inputs
stations and organizations in the vicinity of the aircraft so that alarms
from sensors such as parking brakes, doors, and strut switch senare activated and suitable search and rescue units/forces may be actisors are used to detect OOOI events. At commencement of each
vated to manoeuvre the aircraft to safety. Besides a system by which
flight phase, an ACARS message is transmitted to the ground
the aircraft could be tracked by ground based radar would be activatgiving information about the flight phase, the time at which it
ed and information shared in real time between concerned agencies.
occurred, and other related information, such as the flight origin,
It should also become mandatory that prior to takeoff, the crew will
its destination, and amount of fuel left on board, etc. These meshave to feed in the entire flight plan/path for the sortie.
sages are used to track the status of crew and aircraft.
AUGUST 2017

IEEE A&E SYSTEMS MAGAZINE

Table of Contents for the Digital Edition of Aerospace and Electronic Systems Magazine August 2017